I've wanted to build one of these for some time now. And I am hoping that some of the more inteligent folks here might have some ideas.....Probably on how to use existing methods and synth technology to do this.

Its basically a pair of oscilators (Stereo left and right) that opperate at certain different frequencies (See info on binaural beats below, and click the links) and output through a pair of stereo headphones (It only works via fully stereo-seperated headphones, not through speakers)

There ARE gadgets out there on the market that do all of this....but I think they are over-priced junk....and obviously not nearly as fun as building one DIY style.

So, two oscilators, and maybe some kind of PLL or controller that is set to provide the frequencies differentiated enough to provide the desired binarual beat. (If that makes any sense)

ALSO, maybe a simple white noise generator that can make rain, or waterfall, "relaxing" type sounds.

OR/And, maybe a feature where a stereo (or mono, whatever) audio signal from a CD player can be fed into it, and then the left and right shifted enough to provide the binaural deifference/freqs.

Stimulating the brain with binaural beat frequencies
The easiest way of applying stimulus to the brain is via ears. Other senses could be used as well, and vision is actually used quite often (often in addition to hearing). However, humans cannot hear sounds low enough to be useful for brain stimulation, so special techniques must be used. One such special technique used is called binaural beats.

If the left ear is presented with a steady tone of 500Hz and the right ear a steady tone of 510Hz, these two tones combine in the brain. The difference, 10Hz, is perceived by the brain and is a very effective stimulus for brainwave entrainment. This 10Hz is formed entirely by the brain. When using stereo headphones, the left and right sounds do not mix together until in your brain. The frequency difference, when perceived by brain this way, is called a binaural beat.

I see the challenge in creating dynamical control of the binaural beat; both technical and conceptual. As the brain is very good in accomodating to changing conditions I think a certain randomizing of the modulation-source is needed. Another aspect is the different processing of sustained and pulsed sounds in the brain. Where long sustained sounds tend to create mental rejection - or "passing away of the listener" pulsating sounds stimulate more activation. I think most of the commercial "brain-sync" cd's just use an ongoing detuned low-freq sound as a so called Entrainment matrix".
Perhaps the word sounds more scientifical than the actual technique is. On www.mindalive.com you can find some interesting studies about audio-visual entrainment, which is also interesting from a pure audio perspective.
Best wishes
Pieter

The ramp effect is the most important part of the Hemi-synch (A registered trademark name for using Binaural frequencies for brain wave entrainment)
in most modern machines. The specific frequencies are clinically established for achieving Alpha, Theta or other states and shifting between them smoothly is an art. Incidently, Beta waves can also be generated. Theta Technology Inc. sells a small unit for less than 200$ thats cheaper than a soft synth, less than 400 will get you a deluxe model. The use of light goggles along with the pulsed sound makes a wild experience. I started experimenting with BWE (Brainwave entrainment) in the 1970's and recall when the Alpha Pacer cost over 1k. The first unit I saw was at a US Navy facility and resembled a large chair with multiple speakers. Head phones give exellent results though.

The software is more important than the hardware to a large degree. Of several brands of BWE devices (sold explicitly for that purpose), I only found about three that had the flexibility and sound design that was flexible enough to achieve optimum states. In the 1980's after a few human subjects experienced negative psychological reactions and responses, myself and others informed Theta Tech and a disclaimer was placed on all models sold with that particular set of programs. It seemed that certain pre-existing conditions (Schizophrenia and psychosis mostly) were triggered by the patterns. I of course, still have my early model machine. Some machines allow you to change the values your own self using a computer, thats awesome, presets only go so far as any synth player can tell you!

Programming the mind is an interesting hobby for some of us. Good luck with the experiment!

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